JP2006157710A - Alteration detection threshold deciding system, evaluation target data creating apparatus, threshold-deciding apparatus, evaluation target data creating method and threshold deciding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method etc. for deciding the threshold of difference in image feature amount to be used for determining the presence or the absence of tampering. <P>SOLUTION: This system is provided with a region storage unit 120 for storing region information, including storing image specifying information of the arbitrary region of an original image and the positional information of the region; mark-inserting unit 104 for inserting a mark into the original image; printing-outputting unit 106 for printing the original image; reading unit 108 for creating a read image from a printed matter; mark-detecting unit 112 for detecting the positional information of the mark from the read image; positional information calculating unit 114 for calculating the positional information of a region, corresponding to the arbitrary region of the original image in the read image, on the basis of the region information and the positional information of the mark; image-segmenting unit 116 for segmenting into images from the original image and the read image; evaluation target data output unit 118 for outputting evaluation target data, including the pair of segmented images and image specifying information of each of the images; and threshold-deciding unit 212 for deciding the threshold, on the basis of the evaluation target data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a falsification detection threshold value determination system, an evaluation target data generation device, a threshold value determination device, an evaluation target data generation method, and a threshold value determination method for determining a threshold value for determining whether or not the printed content of a printed matter has been falsified.

  There is a need for a device that can determine whether a document printed on a paper medium has been tampered with. The following technologies are known as devices that can determine whether or not tampering has occurred.

[1] JP 2000-232573 “Printing apparatus, printing method, and recording medium”
When printing the print data on at least the printed matter including the form, by printing the digital watermark corresponding to the print data in addition to the print data, the printed file can be faithfully reproduced just by looking at the printed matter. In addition, it is possible to determine whether or not the print result has been tampered with from the electronic watermark information printed on the printed matter. The determination of tampering is performed by comparing the print result with the one printed with the digital watermark.

  According to the above-described apparatus, in order to determine whether or not tampering has occurred, it is necessary to visually compare the print content extracted from the digital watermark with the print content printed on the paper surface, and there is a possibility that the tampering may be missed due to human error. Therefore, there is a need for a method for automatically determining whether or not tampering has occurred, not by visual inspection. In order to determine automatically, a method of using the feature quantity of the original document and the feature quantity of the document after printing and determining the presence / absence of alteration based on the difference between the feature quantities can be considered. Specifically, it is possible to automatically determine the presence / absence of falsification by setting a threshold value for determining whether or not falsification has occurred and comparing the difference between the feature amounts and the threshold value.

JP 2000-232573 A

  However, there is a problem that the threshold value must be set to an appropriate value when the tampering determination is automatically performed using the feature amount. In particular, when a printed document is input to the computer again by an input device such as a scanner, the input image contains many noise components due to image deformation such as dirt on the printed document and rotation that occurs during input. It is. Therefore, the difference between the feature value of the original document and the feature value of the input image becomes large, and depending on the set threshold value, erroneous detection of falsification that may determine that an unmodified document has been altered may occur. There is sex. On the other hand, if a value that can prevent false detection of falsification is set as a threshold, there is a possibility that a falsification miss that determines that a falsified document has not been falsified may occur.

  Accordingly, the present invention has been made in view of such problems, and the object of the present invention is to automatically determine whether or not tampering has occurred using the feature amount of the image before printing and the feature amount of the image after printing. An object of the present invention is to provide a falsification detection threshold value determination system, an evaluation object data creation device, a threshold value determination device, an evaluation object data creation method, and a threshold value determination method capable of determining an appropriate threshold value.

  In order to solve the above-described problem, according to an aspect of the present invention, there is provided a falsification detection threshold value determination system for determining a threshold value for determining whether or not a print content of a printed matter has been falsified. A region storage unit that stores a plurality of pieces of region information in which image specifying information of a region and position information of the region are associated; marks are inserted into at least two opposing corners of the four corners of the original image A mark insertion unit; an image output unit that outputs the original image in which the mark is inserted; a reading unit that reads a printed matter on which the output original image is printed and creates a read image; and the mark from the read image A mark detection unit for detecting the position information in which the image is inserted; the position information of an arbitrary area of the original image and the position information of the mark based on the position information of the mark A position information calculation unit for calculating position information of an area corresponding to an arbitrary area of the original image; and cutting out an image of the arbitrary area from the original image based on position information of the arbitrary area of the original image; and An image cutout unit that cuts out an image of a region corresponding to the calculated position information from the read image; an evaluation that outputs evaluation target data including the cut out set of images and image specifying information of each image Determining whether or not the image specifying information included in the set of images is the same from the image specifying information of each image included in the evaluation target data; There is provided a falsification detection threshold value determination system comprising: a threshold value determination unit that determines the threshold value based on a set of images.

  According to the above invention, since the mark is inserted into at least two opposing corners of the four corners of the original image by the mark insertion unit, if the mark is detected by the mark detection unit from the read image of the printed matter , Position information of the original image portion in the read image can be obtained. By using the position information, the position information calculation unit can calculate the position information of the area on the read image corresponding to an arbitrary area of the original image. Therefore, even when the printed matter includes a portion other than the original image, for example, a margin or another image, it is possible to acquire position information on the read image corresponding to the original image. Note that even if there is a margin around the original image after printing, or even if another image is included in the same printed material, the mark can be used as a ruled line or a line if it is known which part of the printed material is the original image. Anything such as a digital watermark can be used.

  Further, the image cutout unit can cut out an image of a region on the read image corresponding to any arbitrary region of the original image based on the position information calculated by the position information calculation unit. The image cutout unit also cuts out an image of an arbitrary area from the original image. The image specifying information included in the image cut out from the original image can be specified based on the area information stored in the area storage unit. Further, the image specifying information included in the image cut out from the read image can also be specified from the area information stored in the area storage unit based on the corresponding area of the original image. Therefore, the evaluation target data output unit can acquire a pair of images and specific information of each image. Similarly, the pair of images included in the evaluation target data are images including the same image specifying information or different image specifying information depending on the image specifying information of each image included in the evaluation target data. It is possible to determine whether they are between each other. Therefore, the threshold value determination unit can determine a threshold value for determining whether or not an image has been tampered with using a set of images in which it is known in advance whether the images are similar images or different images. it can.

  According to the above configuration, it is possible to create a plurality of evaluation target data whose presence or absence of falsification is known in advance from one original image.

  In order to solve the above-described problem, according to another aspect of the present invention, there is provided a falsification detection threshold value determination system for determining a threshold value for determining whether or not a print content of a printed matter has been falsified. An area storage unit for storing a plurality of area information in which image specifying information of the area and position information of the area are associated; information on the coordinates in association with a point specified by the coordinates included in the position information; A coordinate information embedding unit that is embedded in an image; an image output unit that outputs an original image in which the coordinate information is embedded; a reading unit that reads a printed matter on which the output original image is printed, and creates a read image; A coordinate information extraction unit for extracting the embedded coordinate information from the read image; based on position information of an arbitrary area of the original image and the extracted coordinate information; A position information acquisition unit that acquires position information of an area corresponding to an arbitrary area of the original image in the read image; and from the original image based on position information of the arbitrary area of the original image; An image cutout unit that cuts out an image and cuts out an image of a region corresponding to the acquired position information from the read image; an evaluation including the set of cut out images and image specifying information of each image An evaluation target data output unit for outputting target data; and determining whether or not the image specification information included in the set of images is the same from the image specification information of each image included in the evaluation target data A falsification detection threshold value determination system comprising: a threshold value determination unit that determines the threshold value based on a determination result and the set of images.

  According to the above invention, the coordinate information embedding unit embeds information on the coordinates in association with a point on the original image having coordinates for specifying an arbitrary area of the original image. Therefore, when the coordinate information extraction unit extracts the coordinate information from the read image of the printed matter, the position information acquisition unit acquires the coordinates in the read image of the point on the read image from which the coordinate information is extracted. In the read image, the position information of the area corresponding to the arbitrary area of the original image can be acquired. Therefore, even if the printed matter contains parts other than the original image, such as margins or other images, or if the original image in the scanned image is rotated, deformed, or distorted, the original image can be handled. It is possible to acquire position information on the read image. Note that the coordinate information may be embedded as a digital watermark.

  Further, the image cutout unit can cut out an image of a region on the read image corresponding to any arbitrary region of the original image based on the position information acquired by the position information acquisition unit. The image cutout unit also cuts out an image of an arbitrary area from the original image. The image specifying information included in the image cut out from the original image can be specified based on the area information stored in the area storage unit. Further, the image specifying information included in the image cut out from the read image can also be specified from the area information stored in the area storage unit based on the corresponding area of the original image. Therefore, the evaluation target data output unit can acquire a pair of images and image specifying information of each image. Similarly, the pair of images included in the evaluation target data are images including the same image specifying information or different image specifying information depending on the image specifying information of each image included in the evaluation target data. It is possible to determine whether they are between each other. Therefore, the threshold value determination unit can determine a threshold value for determining whether or not an image has been tampered with using a set of images in which it is known in advance whether the images are similar images or different images. it can.

  According to the above configuration, it is possible to create a plurality of evaluation target data whose presence or absence of falsification is known in advance from one original image.

  The falsification detection threshold value determination system is an area on the read image in which an image cut out from the read image by the image cutout unit is specified by position information of an area corresponding to an arbitrary area of the original image. And a falsified image creating unit that creates a falsified image by pasting in an arbitrary region different from the cut-out source of the cut-out image; a falsified region storage unit that stores position information of the paste-destination region; May be further provided. According to such a configuration, it can be understood in advance that an image cut out from an arbitrary area of the original image and an image cut out from an area on the read image corresponding to the arbitrary area are different. Therefore, a falsified image in which a falsified area is known in advance can be automatically created from one original image.

  The falsification detection threshold value determination system includes: a feature amount measuring unit that measures each feature amount of the set of images included in the evaluation target data; and a feature amount that obtains a difference value between the measured feature amounts of the images. Based on the image specifying information of each image included in the evaluation object data, either the first group in which the image specifying information of the set of images is the same or the second group that is not the same A tabulation target data storage unit that stores a plurality of the difference values in association with each other; a frequency distribution of the difference values associated with the first group based on the storage content of the tabulation target data storage unit and / or the A totalization unit that creates a frequency distribution of the difference values associated with the second group, and the threshold value determination unit determines the threshold value based on one or both of the frequency distributions It may be configured to.

  According to this configuration, the threshold value determination unit calculates the frequency distribution of the difference value of the feature amount when the included image specifying information is the same and / or the difference value of the feature amount when the included image specifying information is different. A threshold is determined based on the frequency distribution. Therefore, for example, a value larger than that value can be determined as the threshold value so that it is not determined that there is falsification depending on a value frequently taken by a difference in feature amounts when the image specifying information is the same. Further, for example, a value smaller than that value can be determined as the threshold value so that it is not determined that there is no falsification depending on a value that is frequently taken by a difference in feature amount when image specifying information is different.

  The feature amount measuring unit may measure a value output as a feature amount by applying one or more feature extraction filters that strongly react to a specific shape to each image.

  The tampering detection threshold value determination system may include a parameter input unit that inputs a parameter, and the threshold value determination unit may be further configured to determine the threshold value based on the parameter. According to such a configuration, the user can change the threshold value by inputting a parameter.

  The parameter may be a tampering error detection rate, a tampering miss rate, or a probability of determining that tampering has occurred. According to such a configuration, the threshold value can be changed depending on the detection object of alteration. For example, in the case where it is difficult to miss the alteration, the user may input a parameter that increases the probability of determining that the alteration has occurred.

  The falsification detection threshold value determination system includes a falsification region detection unit that detects one or more falsification regions from the falsification image based on the original image, the falsification image, and the threshold value; and is detected by the falsification region detection unit. An accuracy evaluation unit that compares the position information of the one or more tampered areas with the position information of the pasted area, and obtains the accuracy of tampering detection by the tampered area detection unit based on the comparison result; May be provided. According to this configuration, it is possible to evaluate whether or not the threshold value determined by the threshold value determination unit is appropriate.

  In order to solve the above-described problem, according to another aspect of the present invention, there is provided an evaluation object data creation device for creating evaluation object data for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with. A region storage unit that stores a plurality of pieces of region information in which image specifying information of an arbitrary region of the printable original image is associated with the position information of the region; and at least facing the four corners of the original image A mark insertion unit that inserts a mark at two corners; an image output unit that outputs an original image in which the mark is inserted; and a read that reads a printed matter on which the output original image is printed, and creates a read image A mark detection unit that detects position information where the mark is inserted from the read image; based on position information of an arbitrary area of the original image and position information of the mark A position information calculation unit that calculates position information of an area corresponding to an arbitrary area of the original image in a read image; and an image of the arbitrary area from the original image based on position information of the arbitrary area of the original image And an image cutout unit that cuts out an image of a region corresponding to the calculated position information from the read image; the set of cut out images, and image specifying information of each image There is provided an evaluation object data creation device comprising: an evaluation object data output unit for outputting data.

  According to the above invention, it is possible to create a plurality of evaluation target data whose presence or absence of falsification is known in advance from one original image.

  In order to solve the above-described problem, according to another aspect of the present invention, there is provided an evaluation object data creation device for creating evaluation object data for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with. An area storage unit that stores a plurality of area information in which image specifying information of an arbitrary area of the printable original image and position information of the area are associated; a point specified by coordinates included in the position information; A coordinate information embedding unit that embeds the coordinate information in the original image in association with each other; an image output unit that outputs the original image in which the coordinate information is embedded; and a printed matter on which the output original image is printed. A reading unit for creating an image; a coordinate information extracting unit for extracting the embedded coordinate information from the read image; a position information of an arbitrary region of the original image and the extraction A position information acquisition unit that acquires position information of an area corresponding to an arbitrary area of the original image in the read image based on the coordinate information, and the position information acquisition unit based on the position information of the arbitrary area of the original image; An image cutout unit that cuts out an image of the arbitrary region from the original image and cuts out an image of the region corresponding to the acquired position information from the read image; the set of cutout images; and And an evaluation object data output unit for outputting evaluation object data including image specifying information. An evaluation object data creating apparatus is provided.

  According to the above invention, it is possible to create a plurality of evaluation target data whose presence or absence of falsification is known in advance from one original image.

  In order to solve the above-described problem, according to another aspect of the present invention, there is provided a threshold value determination device for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with: a set of images, An evaluation target data input unit that inputs evaluation target data including image specifying information; a feature amount measurement unit that measures each feature amount of the set of input images; and a feature of each measured image A feature amount difference calculating unit for obtaining a difference value between the amounts; a first group in which the image specifying information of the set of images is the same based on the image specifying information of the images included in the evaluation target data; or the same An aggregation target data storage unit that stores a plurality of the difference values in association with any one of the second groups that are not; the difference associated with the first group based on the storage contents of the aggregation target data storage unit Value frequency minutes And / or a totaling unit that creates a frequency distribution of the difference values associated with the second group; and a threshold value determining unit that determines the threshold value based on one or both of the frequency distributions. A threshold value determination device is provided.

  According to the above invention, based on the frequency distribution of the difference value of the feature amount when the included image specifying information is the same and / or the frequency distribution of the difference value of the feature amount when the included image specifying information is different. Determine the threshold. Therefore, for example, a value larger than that value can be determined as the threshold value so that it is not determined that there is falsification depending on a value frequently taken by a difference in feature amounts when the image specifying information is the same. Further, for example, a value smaller than that value can be determined as the threshold value so that it is not determined that there is no falsification depending on a value that is frequently taken by a difference in feature amount when image specifying information is different.

  In order to solve the above-described problem, according to another aspect of the present invention, there is provided an evaluation target data creation method for creating evaluation target data for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with. A region storage step of storing a plurality of region information in the storage unit in association with image specifying information of an arbitrary region of the printable original image and position information of the region; among the four corners of the original image; A mark insertion step of inserting a mark into at least two opposite corners; an image output step of outputting the original image in which the mark is inserted; a printed matter on which the output original image is printed; A reading step of creating; a mark detecting step of detecting position information where the mark is inserted from the read image; and position information of an arbitrary area of the original image. And a position information calculating step of calculating position information of an area corresponding to an arbitrary area of the original image in the read image based on position information of the mark; and based on position information of an arbitrary area of the original image Cutting out an image of the arbitrary area from the original image, and cutting out an image of the area corresponding to the calculated position information from the read image; and the set of cut out images, An evaluation object data generation method is provided, comprising: an evaluation object data output step for outputting evaluation object data including image specifying information of an image.

  In order to solve the above-described problem, according to another aspect of the present invention, there is provided an evaluation target data creation method for creating evaluation target data for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with. A region storage step of storing a plurality of region information in the storage unit in association with image specifying information of an arbitrary region of the printable original image and position information of the region; specified by coordinates included in the position information A coordinate information embedding step for embedding the coordinate information in the original image in association with a point to be printed; an image output step for outputting the original image in which the coordinate information is embedded; and a printed matter on which the output original image is printed. A reading step for reading and creating a read image; a coordinate information extracting step for extracting the embedded coordinate information from the read image; A position information acquisition step of acquiring position information of an area corresponding to an arbitrary area of the original image in the read image based on position information of an arbitrary area of the image and the extracted coordinate information; An image cutout step of cutting out the image of the arbitrary area from the original image based on the position information of the arbitrary area of the image and cutting out the image of the area corresponding to the acquired position information from the read image; There is provided an evaluation object data generation method comprising: an evaluation object data output step for outputting evaluation object data including the set of images and image specifying information of each image.

  In order to solve the above-described problem, according to another aspect of the present invention, there is provided a threshold value determination method for determining a threshold value for determining whether or not a print content of a printed material has been tampered with: An evaluation target data input step for inputting evaluation target data including image specifying information; a feature amount measurement step for measuring each feature amount of the set of input images; and a feature of each measured image A feature amount difference calculating step for obtaining a difference value between the amounts; a first group in which the image specifying information of the set of images is the same based on the image specifying information of the images included in the evaluation target data; or the same An aggregation target data storage step of storing a plurality of the difference values in a storage unit in association with any one of the second groups that is not; and based on the storage contents of the aggregation target data storage unit, A tabulation step of creating a frequency distribution of the assigned difference values and / or a frequency distribution of the difference values associated with the second group; and setting the threshold based on one or both of the frequency distributions A threshold determination method is provided, comprising: a threshold determination step for determining.

  As described above, according to the present invention, it is possible to determine an appropriate threshold value in order to automatically perform the falsification determination using the feature amount of the image before printing and the feature amount of the image after printing. It is possible to provide a possible falsification detection threshold value determination system, evaluation object data creation device, threshold value determination device, evaluation object data creation method, and threshold value determination method.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  The falsification threshold determination system according to the present embodiment uses a device, a program, or the like that detects whether or not an image after printing has been falsified using the feature amount of the image before printing and the feature amount of the image after printing. It is a system for determining a threshold value used for the presence / absence determination. Specifically, a device or program that detects falsification (hereinafter referred to as a falsification detection device) determines that there is no falsification if the difference between the feature amounts of both images is smaller than the threshold value determined by this system. However, if it is greater than the threshold value, it is a system for determining an appropriate threshold value that makes it possible to more accurately determine whether or not tampering has occurred.

  The falsification detection threshold value determination system according to the present embodiment includes a threshold value determination device 20 that determines a threshold value for determining whether or not a print content of a printed matter has been falsified, and evaluation target data generation that generates evaluation target data for determining the threshold value. The apparatus 10 and the evaluation apparatus 30 which evaluates the tampering detection accuracy by the determined threshold value are provided. The threshold value determination device 20 determines the threshold value using the evaluation object data created by the evaluation object data creation device 10, and causes the falsification detection device or the like to perform falsification detection using the threshold value determined by the threshold value determination device, The accuracy evaluation device 30 performs the accuracy evaluation.

  In order to determine an appropriate threshold value, a plurality of pre-printed images, an image obtained by printing the image, or an image obtained by printing and modifying the image are used, and the tampering is performed while appropriately changing the threshold value. It is necessary to perform detection and find a threshold value with which the detection result is more accurate. Conventionally, it is necessary to manually create an image that has been printed from multiple pre-printed images and an image that has been printed and tampered with, and find the optimal threshold while manually changing the threshold appropriately. was there. According to the falsification detection threshold value determination system according to the present embodiment, the evaluation target data creation device 10 creates an image obtained by printing the image from a plurality of pre-print images, or an image obtained by adding the alteration by printing the image. Then, the threshold value determination device 20 automatically determines the optimum threshold value so that the threshold value can be determined easily and quickly.

  In the present embodiment, as described above, the evaluation target data creation device 10, the threshold value determination device 20, and the accuracy evaluation device 30 constitute a tampering detection threshold value determination system. By providing, this system may be comprised by one apparatus. Further, each function described later of each device may be distributed to a plurality of devices other than the above three devices, and this system may be configured from a plurality of devices.

  Hereinafter, the falsification detection threshold value determination system according to the present embodiment will be described in detail. First, the functional configuration of each device included in the tampering detection threshold value determination system will be described with reference to FIGS.

  FIG. 1 is a block diagram showing a functional configuration of the evaluation object data creation device 10. The evaluation target data creation device 10 includes, for example, a test chart generation unit 102, a mark insertion unit 104, a print output unit 106, a reading unit 108, a mark detection unit 112, a position information calculation unit 114, and an image cutout unit. 116, an evaluation object data output unit 118, a region storage unit 120, a read image region storage unit 122, a falsified image creation unit 124, a falsified region storage unit 126, and the like.

  The test chart generation unit 102 has a function of creating a test chart image, which is an example of an original image that is a source of evaluation target data, and storing information about an arbitrary region of the test chart image in the region storage unit 120 as region information. . Specifically, text data of characters and symbols input by a user is obtained from an input means such as a keyboard provided in the evaluation object data creation apparatus 10, and a document image is obtained by converting a document including the plurality of text data. A test chart image is created. Note that the evaluation target data creation device 10 may generate a document image using text data of a font of a type or size designated by the user or the like. The test chart generation unit 102 stores the image specifying information of an arbitrary region of the generated test chart image and the position information of the region in the region storage unit 120 in association with each other. In the present embodiment, the above-described text data is used as an example of the image specifying information. That is, the test chart generation unit 102 associates text data such as characters and symbols included in an arbitrary area with the coordinates indicating the position information of the area and stores them in the area storage unit 120.

  The mark insertion unit 104 has a function of inserting marks into at least two opposite corners of the four corners of the test chart image. In this embodiment, the mark is a digital watermark, and the mark insertion unit 104 embeds the digital watermark in the entire area including the four corners of the test chart image. The mark may be anything such as a ruled line surrounding the outer frame of the test chart image as long as the test chart image portion can be specified from the printed matter when the test chart image is printed. Even when the mark is a digital watermark, the mark may not be embedded in the entire area of the test chart image as in the present embodiment, but may be embedded only in at least two opposing corners among the four corners. In the present embodiment, the mark insertion unit 102 embeds a digital watermark in the entire area of the test chart image, and a mark detection unit 112 (to be described later) uses a digital watermark from a read image created by reading a printed matter on which the test chart image is printed. By detecting the area in which is embedded, the test chart image portion can be identified from the printed matter.

  In order for the mark insertion unit 104 to embed a digital watermark in the test chart image and the mark detection unit 112 to detect a region where the digital watermark is embedded from the read image, for example, the following digital watermark technology can be used. In the present embodiment, since the digital watermark is only used for detecting the test chart image portion in the printed matter, any information can be embedded in the test chart image as the digital watermark.

  For example, as disclosed in Japanese Patent Application Laid-Open No. 2003-209676, “Digital Watermark Embedding Device, Digital Watermark Detection Device, Digital Watermark Embedding Method, and Digital Watermark Detection Method”, the digital watermark technology uses an arbitrary dot pattern. Is a technology that embeds the image in paper and transmits information as a digital watermark in addition to physical information for visual inspection.

  Digital watermarking technology not only embeds arbitrary information on paper, but also the small unique patterns to be embedded themselves indicate the positional relationship between the patterns or relative to the paper, and after the image is read by a scanner or the like. This is used as a reference for correcting the image.

  FIG. 26 is an explanatory diagram for explaining an arbitrary pattern to be embedded in a digital watermark. Referring to FIG. 26, an image based on such digital watermark is represented as a set of N unit patterns composed of a plurality of small dots. Each unit pattern corresponds to a numerical value of 0 to N−1. For example, the unit pattern 902 represents a numerical value 0 and the unit pattern 904 represents a numerical value 1. The unit pattern can be expressed in black and white or color.

  FIG. 27 is an external view for explaining an image (paper) printed with a digital watermark. Referring to the entire sheet of FIG. 27, the image based on the digital watermark can be divided into a main area 910, an attribute information area 912, and a boundary information area 914 depending on the role of the image. The main area 910 is a main area for embedding information. The attribute information area 912 stores information necessary for reading the information embedded in the main area 910, such as the size of the area in which the digital watermark is embedded and the information encoding method in the main area 910. A predetermined specific unit pattern is printed in the boundary information area 914, and the reading side can identify the boundary of the digital watermark by this area.

  On the reading side such as a scanner, the paper printed in this way (hereinafter simply referred to as digital watermark paper) is scanned to detect individual unit patterns embedded in the paper. This detection is performed using template matching or a two-dimensional filter (for example, a two-dimensional Gabor filter) having a filter characteristic for an arbitrary directionality and shape.

  Further, when embedding a digital watermark in the paper, specific unit patterns are regularly arranged at specific positions in the boundary information area 914 and the main area 910. Thus, on the paper reading side, these unit patterns for position detection can be extracted and correction can be performed based on the position information. Therefore, the original image can be restored without performing troublesome manual correction even if the scanned data is displaced due to displacement or rotation or biased due to wrinkles.

  In addition, when printing or scanning, a part of the unit pattern may be stained with, for example, ink and cannot be detected. Therefore, in the main area 910, information to be embedded is distributed at a plurality of locations, or is embedded with an error resilience code (parity check code, Hamming code, BCH code, etc.) as disclosed in Japanese Patent Laid-Open No. 2003-209676. For example, even if a part of the unit pattern is missing, the information can be restored.

  Returning to FIG. 1, the description of the functional configuration of the evaluation object data creation device 10 will be continued. The print output unit 106 has a function of printing a test chart image in which a digital watermark is embedded. The print output unit 106 is an example of an image output unit. The image output unit may print a test chart image as in the present embodiment, or may output it as an electronic data to an external recording medium such as a CD (Compact Disk) or a flexible disk. Alternatively, the electronic data may be transmitted to an external computer connected via a communication network such as a LAN (Local Area Network).

  The reading unit 108 has a function of reading a printed matter on which a test chart image is printed and creating a read image. Specifically, the printed matter is read through a reading unit such as a scanner, and a read image is created based on the read data. The printed matter on which the test chart image is printed may include a margin portion in addition to the test chart image portion. However, such a margin portion is included in the read image created by the reading unit 108. include. Also, the test chart image may be reduced during reading.

  The mark detection unit 112 has a function of detecting position information where a mark is inserted from the read image. Specifically, the boundary of the digital watermark embedded in the read image is identified by using the boundary information area. Then, the position information in the read image of the area divided by the boundary, that is, the area in which the digital watermark is embedded (hereinafter also referred to as a watermark area) is, for example, the coordinates of the start position and the end position of the area. And detect by getting. In this embodiment, since the digital watermark is embedded in the entire area of the test chart image, the coordinates of the start position of the watermark area in the test chart image before printing are (0, 0). Since the read image may include a blank portion as described above, the start position of the watermark region is not always (0, 0).

  The position information calculation unit 114 has a function of calculating position information of an area corresponding to an arbitrary area of the test chart image in the read image based on position information of an arbitrary area of the test chart image and position information of the mark. . Specifically, the position information calculation unit 114 acquires the region information stored in the region storage unit 120, coordinates included in the region information, coordinates for specifying the watermark region detected by the mark detection unit 112, and Based on the above, the coordinates for specifying the area on the read image corresponding to the area on the test chart image before printing specified by the coordinates included in the area information are obtained. When acquiring the area on the read image corresponding to the area on the test chart image, if the coordinates specifying the area on the test chart image are used as they are, the read image includes a margin as described above. Since the start position of the test chart image is shifted, a different area is acquired. Therefore, by calculating using the position information of the watermark area, it is possible to acquire the corresponding area even when the start position is shifted due to the margin part.

  Further, the position information calculation unit 114 may calculate the position information in consideration of the difference in size between the test chart image before printing and the test chart image in the read image. The combination of the start position (0, 0) and end position of the test chart image, or the size of the test chart image is stored in the area storage unit or other storage unit by the test chart generation unit 102, for example, or the mark insertion unit By embedding the above information (combination or size of start position and end position) in the test chart image, the position information calculation unit 114 can acquire the size of the test chart image. Since the position information calculation unit 114 can also acquire the size of the watermark area from the position information of the watermark area detected by the mark detection unit 112, the ratio between the size of the test chart image before printing and the size of the watermark area is set. The position information can be calculated in consideration of the difference in size between the test chart image before printing and the test chart image in the read image.

  The read image area storage unit 122 stores read image area information in which the position information calculated by the position information calculation unit 114 and the image specifying information (text data) included in the area specified by the position information are associated with each other. It is remembered.

  The image cutout unit 116 cuts out an image of the arbitrary region from the test chart image based on the position information of the arbitrary region of the test chart image, and is specified by the position information calculated by the position information calculation unit 114 The image is read out and cut out from the image. Specifically, the image cutout unit 116 acquires arbitrary region information from the region storage unit 120, and cuts out an image of the region specified by the coordinates included in the region information (hereinafter also referred to as a cutout image from the original image). .) Further, arbitrary read image area information is acquired from the read image area storage unit 122, and an image of an area specified by coordinates included in the read image area information is cut out (hereinafter also referred to as a cut image from the read image). . In this specification, to cut out the image of the area specified by the coordinates, the image of the specific area is cut or copied from the test chart image or the read image, and the cut or copied image is left as it is or of the size. This means that the image is changed into one image by changing or binarizing it. Therefore, a plurality of images can be created from one test chart image or read image. Hereinafter, the mark detection unit 112, the position information calculation unit 114, and the image cutout unit 116 are collectively referred to as an evaluation image generation unit 110.

  The evaluation target data output unit 118 has a function of outputting evaluation target data including a set of images cut out by the image cutout unit 116 and image specifying information of each image. Specifically, the evaluation target data output unit 118 acquires from the image cutout unit 116 a cutout image from the original image, a cutout image from the read image, and image specifying information included in each image, One set of data for evaluation is output to an external recording medium such as a CD. The image specifying information included in each image is searched from the area storage unit 120 or the read image area storage unit 122 for the image specifying information stored in association with the area of the image cut out by the image cutting unit 116. Can be obtained by: Note that the evaluation target data output unit 118 does not output the evaluation target data to the external recording medium as described above, but transmits the evaluation target data to the threshold value determination device 20 that determines the threshold value using the evaluation target data. You may make it memorize | store in the memory area which can be referred to the threshold value determination apparatus 20 inside or outside the data preparation apparatus 10.

  The falsified image creation unit 124 has a function of creating a falsified image. Specifically, the image cut out from the read image by the image cutout unit 116 is an area on the read image specified by position information of an area corresponding to an arbitrary area of the test chart image, and is cut out. A falsified image is created by pasting it in an arbitrary area different from the cutout source of the image. In other words, the falsified image creation unit 124 acquires a cut-out image from the read image from the image cut-out unit 116, and includes the acquired image in any read image area information stored in the read image area storage unit 122. Paste to the area specified by the coordinates. Note that the pasting is performed on a region different from the region from which the cutout image acquired from the image cutout unit 116 is cut out. With this process, the image specifying information in the pasting area is different before and after the pasting. Therefore, the image specifying information in the pasting area is different from the image specifying information included in the corresponding area of the test chart image. Information will be included. After the above-described pasting process, the falsified image creation unit 124 includes position information for specifying the pasting area, image specifying information for the area before pasting, and image specifying information for the same area after pasting. It is stored in the falsified area storage unit 126 as falsified area information. Note that only the position information specifying the pasting area may be stored in the falsified area storage unit 126. Further, the alteration area information may not be stored in the alteration area storage unit 126, but may be embedded as a digital watermark in the alteration image.

  The functional configuration of the evaluation target data creation device 10 has been described above. Next, a functional configuration of the threshold value determination device 20 according to the present embodiment will be described with reference to FIG.

  The threshold determination device 20 includes, for example, an evaluation target data input unit 202, a feature amount measurement unit 204, a feature amount difference calculation unit 206, a total target data storage unit 208, a totalization unit 210, a threshold determination unit 212, and the like. Prepare.

  The evaluation target data input unit 202 has a function of inputting evaluation target data including a set of images and image specifying information of each image. In this embodiment, the evaluation target data output by the evaluation target data creation device 10 is input by reading from an external recording medium in which the evaluation target data is recorded, for example. If the threshold value determination device 20 is connected to the evaluation object data creation device 10 in communication, the evaluation object data may be received via a communication network. Alternatively, evaluation target data stored in an internal or external storage area of the evaluation target data creation device 10 may be read. Note that the set of images and the image specifying information of each image need not be created by the evaluation object data creation device 10.

  The feature amount measuring unit 204 has a function of measuring each feature amount of the input set of images. As a method for measuring the feature amount, a method of obtaining a feature amount of each image by performing a filtering process with a Gabor filter or a known filter on each image and obtaining an average value of the filter output may be applied. it can. Further, the feature amount may be measured in more detail by dividing the image into a plurality of regions and measuring the feature amount for each of the divided regions. Besides the feature quantity measurement by filtering, a method of performing pattern matching by generating a reduced image and measuring the degree of coincidence can be applied. The feature quantity measured from the image is almost the same feature quantity in the same image. However, even if the images are the same, the pre-printed image and the scanned image of the printed material may be smudged, smeared, deformed, etc. depending on the performance of the printer or scanner. In some cases, the feature amount of the image and the feature amount of the read image are different.

  The feature amount difference calculation unit 206 has a function of obtaining a difference value between feature amounts of a set of images measured by the feature amount measurement unit 204. Further, the feature amount difference calculation unit 206 calculates the aggregation target data in which the image specifying information included in each of the set of images whose feature amounts are measured by the feature amount measurement unit 204 and the obtained difference values are associated with each other. The data is stored in the target data storage unit 208. The feature amount difference calculation unit 206 can acquire the image specifying information included in each image by referring to the evaluation target data input by the evaluation target data input unit 202. The feature amount difference calculation unit 206 has the same image specifying information included in a set of images included in the evaluation target data when the image specifying information of the images included in the evaluation target data is the same. The aggregation target data is stored in the aggregation target data storage unit 208 by distinguishing between cases and different cases. Accordingly, the aggregation target data storage unit 208 stores a plurality of difference values in association with either the first group in which the image specifying information of a set of images is the same or the second group that is not the same. Note that the feature amount difference calculation unit 206 stores the image identification information of each image if the aggregation target data is stored in the aggregation target data storage unit 208 so that the first group and the second group can be distinguished as described above. Does not have to be remembered.

  Based on the aggregation target data stored in the aggregation target data storage unit 208, the aggregation unit 210 calculates the frequency distribution of the difference values associated with the first group and the difference values associated with the second group. It has a function to create a frequency distribution.

  The threshold value determination unit 212 has a function of determining a threshold value for determining whether or not tampering has been detected based on one or both of the frequency distributions created by the counting unit 210. Even if the feature values of the image before printing and the read image after printing are different, if the cause of the difference is that the image has been printed and read as described above, the falsification detection device etc. Should not be judged to be present. Therefore, the counting unit 210 generates a frequency distribution of the difference values of the feature values of the first group in which the image specifying information of the set of images is the same and a frequency distribution of the difference values of the feature values of the second group that are not the same. By being created, the threshold value determination unit 212 can acquire a difference value (allowable difference range) that should be determined not to be falsified even if there is a difference between the feature amounts of a set of images. . When the threshold value determination unit 212 determines the value as a threshold value, an alteration detection device or the like that uses the threshold value for determination of whether or not the alteration has occurred can make an appropriate determination.

  Although details will be described later, the threshold value determination unit 212 can set a threshold value that can satisfy the detection accuracy specified by the parameter based on the parameter specified by the user. In the present specification, the tampering detection accuracy is expressed by a tampering miss rate and a tampering detection rate. The falsification miss rate is a probability that a falsification detection device or the like erroneously determines that there is no falsification even though the image to be determined is falsified. The falsification error detection rate is a probability that a falsification detection device or the like erroneously determines that there is falsification even though the image to be determined has not been falsified.

  The functional configuration of the threshold determination device 20 has been described above. Next, the functional configuration of the accuracy evaluation device 30 will be described with reference to FIG.

  The accuracy evaluation apparatus 30 includes, for example, an input unit 302, a falsification region detection unit 304, a falsification region storage unit 305, a falsification detection result region storage unit 306, and an accuracy evaluation unit 308.

  The input unit 302 inputs the test chart image, the falsified image, the position information (falsified region information) of all paste destination regions stored in the falsified region storage unit 126 of the evaluation target data creation device 10 and the threshold value. It has the function to do. Specifically, a test chart image before printing, a read image after falsification (falsification image) created by the falsification image creation unit 124, and falsification area information are acquired from the evaluation target data creation device 10. Further, the input unit 302 acquires the threshold value determined by the threshold value determination unit 212 from the threshold value determination device 20. The input unit 302 stores the acquired falsification area information in the falsification area storage unit 305. The contents stored in the falsified area storage unit 305 are substantially the same as the falsified area storage unit 126 included in the evaluation target data creation unit 10. In the case where the alteration detection threshold value determination system is composed of one device, it is sufficient to provide one alteration region storage unit. In addition, when the falsified area information is embedded in the falsified image, the input unit may have a function of extracting the falsified area information from the falsified image.

  The falsification area detection unit 304 detects one or more falsification areas from the falsification image based on the test chart image, the falsification image, and the threshold value, and the falsification detection result area storage unit 306 detects position information that identifies the detected area. It has a function to write to. The falsification area detection unit 304 obtains falsification detection information from a falsification detection apparatus or the like that is subject to evaluation of falsification detection accuracy in this apparatus, and the position information of the area detected as the falsification area by the apparatus from the apparatus. And a function for writing to the result area storage unit 306. Specifically, a test chart image and a falsified image are provided to a falsification detection device or the like, and the falsification is detected by setting the threshold value of the device to the threshold value input by the input unit 302. Thereafter, the position information of the area detected as the falsified area by the apparatus is acquired from the apparatus, and all the information is written in the falsification detection result area storage unit 306. Note that the falsification detection device or the like is not included in the falsification region detection unit 304, and the falsification region detection unit 304 is configured to acquire a detection result from the falsification detection device or the like via a communication network or a recording medium. Also good.

  The accuracy evaluation unit 308 compares the position information of one or more tampered areas detected by the tampered area detection unit 304 with the position information of the pasted area input by the input unit 302, and compares the comparison results. And a function for obtaining the accuracy of detection of alteration by the alteration region detection unit 304 based on the above. Specifically, the accuracy evaluation unit 308 compares the storage content of the falsification area storage unit 305 and the storage content of the falsification detection result area storage unit 306 to obtain the falsification detection accuracy of the falsification detection device or the like that is the evaluation target. The falsification area storage unit 305 stores position information of an actually falsified area (an area different from the original test chart image), so that the falsification area is determined by the position information and the falsification detection device. By comparing the position information of the detected area, it is possible to know a portion that has missed tampering or a portion that has been erroneously detected, and the accuracy evaluation unit 308 can obtain a tampering miss rate or a tampering misdetection rate.

  The functional configuration of the accuracy evaluation device 30 has been described above. Next, based on FIG. 4 to FIG. 12, the flow of processing of the evaluation target data creation device 10 according to the present embodiment will be described.

  First, the processing flow of the evaluation object data creation device 10 will be schematically described based on FIGS. 4 and 5, and then more detailed description will be given based on FIGS. 6 to 12.

  As shown in FIG. 4, first, text data of characters and symbols is input to the test chart generation unit 102 as evaluation characters. Also, the font type and size are input as output font information (step S102 in FIG. 5). The test chart generation unit 102 creates a test chart image 1002 based on the input data, and associates position information of an area including text data (image specifying information) of one evaluation character with the evaluation character. The stored area information is stored in the area storage unit 120 (step S104).

  The created test chart image 1002 is provided to the mark insertion unit 104, and the mark insertion unit 104 embeds a digital watermark in the entire area of the test chart image 1002 (step S106). The test chart image 1002 in which the digital watermark is embedded is printed by the print output unit 106 (S108), and a printed material 1004 on which the test chart image 1002 is printed is output.

  Thereafter, the printed material 1004 is read by the reading unit 108, and a read image is created (S110). The created read image is provided to the evaluation image generation unit 110, and the evaluation image generation unit 110 generates a pair of images to be evaluated based on the area information and the watermark area stored in the area storage unit 120 ( S112). The evaluation target data output unit 118 outputs evaluation target data 1006 including a pair of images 1010 and 1012 created by the evaluation image generation unit 110 and a combination 1008 of evaluation characters that are image specifying information included in each image. (S114). The outline of the processing flow has been described above.

  Next, a detailed description will be given. As shown in FIG. 6, the test chart image 1002 created by the test chart generation unit 102 includes a plurality of text data of evaluation characters. According to the illustrated example, the area including the evaluation character “0” is an area specified by coordinates (200, 200) and (300, 300). Therefore, in the area storage unit 120, the evaluation character “0” and the position information “200, 200, 300, 300” for specifying the area including “0” are associated and stored as one area information. . Similarly, the area storage unit 120 stores evaluation characters “1” and position information “400, 200, 500, 300” for specifying an area including “1”, evaluation characters “2”, and “2”. Position information “600, 200, 700, 300” for specifying a region to be included is associated with each other, and each is stored as region information.

  As shown in FIG. 7, an electronic watermark is embedded in the entire area of the test chart image 1002 by the mark insertion unit 104, the watermark embedded image 1003 is printed by the print output unit 106, and the test chart image in which the watermark is embedded is printed. The printed material 1004 is output. The printed material 1004 is read by the reading unit 108 as shown in FIG. 8, and a read image 1005 is created. The created read image and the area information stored in the area storage unit 120 are provided to the evaluation image generation unit 110. The evaluation image generation unit 110 includes the mark detection unit 112, the position information calculation unit 114, and the image cutout unit 116 as described above.

  For the read image 1005 provided to the evaluation image generation unit 110, the mark detection unit 112 first performs watermark area detection processing. According to the example of FIG. 9, the detected watermark area is an area specified by coordinates (235, 115) and (3200, 4480) in the read image 1005. Once the watermark area is specified, it becomes possible to calculate the size of the watermark area, and according to the example shown, the size of the watermark area is 2965 × 4365. On the other hand, the test chart image extends from coordinates (0, 0) to (4488, 6543), and its size is 4488 × 6543. Then, the watermark area in the read image 1005, that is, the test chart image portion in the read image 1005 starts from the coordinates (235, 115), and is 2/3 times the size of the original test chart image 1002 before printing. I know that there is.

The position information calculation unit 114 reads the read image based on the information obtained by the watermark detection by the mark detection unit, that is, the start position and size ratio of the watermark region and the region information stored in the region storage unit 120. Create area information. More specifically, according to the example shown in the figure, the coordinates for specifying the region on the read image 1005 corresponding to the region including the evaluation character “0” in the original test chart image 1002 can be obtained by the following calculation. it can.
(200 × 2/3 + 235, 200 × 2/3 + 115, 300 × 2/3 + 235, 300 × 2/3 + 115) = (368, 248, 435, 315) (rounded down)
Similarly, the coordinates specifying the region on the read image 1005 corresponding to the region including the evaluation character “1” in the original test chart image 1002 are (501, 248, 701, 315). Information on these coordinates is stored in the read image area storage unit 122 as read image area information in association with an evaluation character included in the area specified by the coordinates.

  Next, as shown in FIG. 10, the image cutout unit 116 cuts out an image of an arbitrary region from the test chart image based on the coordinate information included in each region information stored in the region storage unit 120. In addition, the image cutout unit 116 cuts out an image of an arbitrary region from the read image based on the coordinate information included in each read image region information stored in the read image region storage unit 122. Each image to be cut out includes one evaluation character. The image cutout unit 116 adjusts the size by enlarging or reducing the cutout set of images and binarizing the set of images and the evaluation characters included in each image. Information (such as “0” or “1”) is provided to the evaluation target data output unit 118. The evaluation target data output unit 118 uses the cut-out image from the test chart image 1002 as the pre-falsification image 1010, the cut-out image from the read image 1005 as the determination target image 1012, and the evaluation characters included in each image as the combination data 1008. A set of evaluation target data is output.

  11 and 12 show the flow of processing for creating a falsified image by the falsified image creating unit 124. As shown in FIG. 11, the falsified image creation unit 124 creates a falsified image using the read image 1005 and the read image area information stored in the read image area storage unit 122. Specifically, as shown in FIG. 12, a falsified image 1007 is created by pasting an image cut out from the read image 1005 by the image cutout unit 116 to another area on the read image 1005, and the paste destination Is stored in the falsified area storage unit 126 as falsified area information. According to the example shown in the figure, an image of an area including “1” specified by coordinates (501, 248) and (568, 315) in the read image is displayed in the read image as coordinates (368, 245) and (435, 345). 315) is pasted to the area including “0”. Then, the coordinates (368, 245) and (435, 315) of the pasting area, the evaluation character “0” included in the area before pasting, and the evaluation character included in the area after pasting “1” is associated and stored in the falsified area storage unit 126. By sequentially performing the above-described pasting process on the area including each evaluation character, it is possible to create a falsified image 1007 in which all evaluation characters included in the read image 1005 are replaced as illustrated.

  The process flow of the evaluation target data creation device 10 according to the present embodiment has been described above. Next, an evaluation target data creation device 40, which is a modification of the evaluation target data creation device 10 according to the present embodiment, will be described focusing on differences from the evaluation target data creation device 10.

  The evaluation target data creation device 40 creates the evaluation target data from the test chart image, similarly to the evaluation target data creation device 10. In the evaluation object data creation device 10, in order to acquire a region on the read image corresponding to an arbitrary region of the test chart image, a digital watermark is embedded in the entire region of the test chart image, and based on the position information and size of the watermark region. The position information of the corresponding area was calculated. On the other hand, the evaluation object data creation device 40 embeds position information for specifying an arbitrary area of the test chart image in the test chart image in association with the actual position in the test chart image, thereby The location information can be acquired. According to such a configuration, when reading a printed matter on which a test chart image is printed, the test chart image in the read image is distorted due to a crease or wrinkle of the printed matter, or the test chart image in the read image is changed due to a deviation in the reading direction. Even if a rotational system shift occurs, the position information of the corresponding region can be obtained accurately. This will be described in detail below.

  FIG. 13 is a block diagram showing a functional configuration of the evaluation object data creation device 40. Components having the same functions as those of the evaluation target data creation device 10 are denoted by the same reference numerals and description thereof is omitted. The coordinate information embedding unit 404 has a function of embedding the coordinate information as a digital watermark in the test chart image in association with the point specified by the coordinates included in the position information stored in the area storage unit 120. Specifically, as shown in FIG. 14, the coordinate information included in the area information stored in the area storage unit 120 is embedded in a point on the test chart image specified by the coordinates. According to the example shown in the drawing, the coordinates (200, 200) of the coordinates of the start point 4002 are embedded as invisible information at the start point 4002 indicating the start position of the region including the evaluation character “0”. Similarly, the coordinates (300, 300) of the end point 4004 are embedded as invisible information at the end point 4004 indicating the end position of the region including the evaluation character “0”.

  The coordinate information extraction unit 412 has a function of extracting coordinate information embedded from the read image. The position information acquisition unit 414 determines the position of the region corresponding to the arbitrary region of the test chart image in the read image based on the positional information of the arbitrary region of the test chart image and the coordinate information extracted by the coordinate information extraction unit 412. Get information.

  Specifically, as shown in FIG. 15, the coordinate information extraction unit 412 searches for embedded invisible information from, for example, the upper left end to the lower right end of the read image, and extracts the information. According to the illustrated example, information indicating (200, 200) embedded in the start point 4002 of the read image and information indicating (300, 300) embedded in the end point 4004 are extracted. The position information acquisition unit 414 acquires the coordinates in the read image of the point from which the information is extracted by the coordinate information extraction unit 412, and creates read image area information based on the storage contents of the area storage unit 120. According to the illustrated example, the start point 4002 from which the information (200, 200) is extracted is a point specified by coordinates (368, 248) on the read image, and the information (300, 300) is The extracted end point 4004 is a point specified by coordinates (435, 315) on the read image. Therefore, the area specified by the coordinates (200, 200) and (300, 300) in the test chart image corresponds to the area specified by the coordinates (368, 248) and (435, 315) on the read image. I understand that. Therefore, the position information acquisition unit 414 associates the position information “368, 248, 435, 315” specifying the corresponding area with the evaluation character “0” included in the area, and reads the read image area information as read image area information. Stored in the unit 122.

  Since the read image area storage unit 122 stores the position information of the area corresponding to an arbitrary area of the test chart image and the evaluation characters included in the area as in the evaluation object data creation device 10, the image cutout unit 116 is stored. The image can be cut out by the same process as the process described above in the evaluation object data creation device 10.

  The evaluation object data creation device 10 may incorporate the coordinate embedding and extraction processing in the evaluation object data creation device 40. In this case, for example, the evaluation object data creation device 10 embeds a digital watermark in the entire area of the test chart image by the mark insertion unit 104. In particular, the point specified by the position information included in the area information includes: The coordinate information of the point is embedded by the coordinate embedding process described above. When acquiring the position information of the corresponding area in the read image, the position information calculation unit 114 may calculate the position information based on the position information and size of the watermark area as described above, or extract the embedded coordinate information. Then, the position information may be acquired.

  The processing performed by the evaluation target data creation device 10 according to the present embodiment and the evaluation target data creation device 40 that is a modification thereof has been described above. Next, based on FIG. 16 to FIG. 22, the flow of processing of the threshold value determination device 20 according to the present embodiment will be described.

  First, the processing flow of the threshold value determination device 20 will be schematically described with reference to FIGS. 16 and 17, and then more detailed description will be made with reference to FIGS.

  A plurality of evaluation object data 1006-1, 1006-2,... 1006-n (hereinafter simply referred to as evaluation object data 1006) and parameters are input to the threshold value determination device 20 (step S202 in FIG. 17). . The feature amount measuring unit 204 uses the feature amounts of a set of images 1010-1 and 1012-1 (hereinafter referred to as pre-falsification images 1010 and determination target images 1012) included in the input evaluation target data 1006. Measure (S204). Based on the measured feature amount of each image, the feature amount difference calculation unit 206 calculates a difference value of the feature amount (S206). The difference values are accumulated in the aggregation target data storage unit 208, and the aggregation unit 210 creates a frequency distribution of the difference values based on the accumulated difference values (S208). When the frequency distribution is created, the threshold value determination unit 212 determines an optimal threshold value based on the frequency distribution and the parameters (S210). The outline of the processing flow has been described above.

  Next, a detailed description will be given. As shown in FIG. 18, evaluation target data 1006 is input by the evaluation target data input unit 202. The input pre-falsification image 1010 and determination target image 1012 are provided to the feature amount measurement unit 204, and the feature amount measurement unit 204 measures the feature amount of each image. As described above, the feature amount can be measured by performing an image filtering process using a Gabor filter or a filter that strongly reacts to a specific shape. According to the illustrated example, the feature amount of the pre-falsification image 1010 is 7, and the feature amount of the determination target image 1012 is 15. Both feature amounts are provided to the feature amount calculation unit 206, and the feature amount calculation unit 206 calculates a difference value. According to the illustrated example, the difference value is 8.

  Thereafter, the calculated difference value is stored in the aggregation target data storage unit 208 as the aggregation target data 2002 together with the combination data 1008. Note that, as described above, if the evaluation target data (image specifying information) included in the combination data 1008 is stored in the aggregation target data storage unit 208 so that it can be seen whether or not they are the same, the combination data 1008 is included in the aggregation target data 2002. May not be included.

  When the above-described processing is performed on a plurality of evaluation object data 1006, a plurality of aggregation object data 2002-1, 2002-2, 2002-3,... 2002-n are aggregation objects as shown in FIG. The data is stored in the data storage unit 208. Aggregation target data 2002-1 and 2002-2 are examples of the aggregation target data created from evaluation target data with different evaluation characters included in the combination data 1008. The image of each image included in the evaluation target data described above. The specific information is stored in association with the second group that is not the same. On the other hand, the aggregation target data 2002-3 and 2002-n are examples of the aggregation target data created from the evaluation target data having the same evaluation character included in the combination data 1008, and are included in the above-described evaluation target data. The image specifying information of each image is stored in association with the same first group. It can be seen that the aggregation target data belonging to the first group has a smaller feature amount difference value than the aggregation target data belonging to the second group.

  After a plurality of aggregation target data is accumulated, the aggregation target data is aggregated by the aggregation unit 210, and a frequency distribution is created as the aggregation result. Specifically, a frequency distribution of feature amount difference values of the aggregation target data belonging to the first group and a frequency distribution of feature amount difference values of the aggregation target data belonging to the second group are respectively created. The frequency distribution can be represented as a histogram as shown in FIG. Alternatively, it may be expressed as a cumulative histogram as shown in FIG. Reference numeral 2010 in the graph denotes a first group histogram, and reference numeral 2012 denotes a second group histogram. In FIG. 19C, the cumulative amount of the first group is reduced from 100%. The graphs shown in FIGS. 19B and 19C show the aggregation results when “Times New Roman” is specified as the font type and “10.5 points” is specified as the font size when the test chart image is generated. ing.

  Referring to FIGS. 19B and 19C, when the image specifying information (text data having a font type of Times New Roman and a font size of 10.5 points) is the same for a set of images, It can be seen that the difference value of the feature amount when the read image is not falsified is about 1.8, and there is almost no value larger than 4. On the other hand, if the image identification information of a set of images is not the same, that is, if the read image of the printed matter has been tampered with, the feature value difference value is often a value in the range of 6 to 10, It turns out that there is almost no small value. The threshold determination unit 212 determines a threshold based on the created histogram.

  FIG. 20 is an example in which the threshold is determined so that the falsification miss rate by the falsification detection device or the like and the falsification error detection rate are equal. The point at which the first group histogram 2010 and the second group histogram 2012 intersect is a threshold at which the falsification miss rate = falsification false detection rate, which is 3.5 according to the illustrated example.

  FIG. 21 shows a case where a threshold value is set so that a false detection rate by a falsification detection device or the like is 5% or less (3.2 according to the illustrated example), or a falsification miss rate is 0.5% or less. A case where the threshold value is set so as to be (in the example shown, 2.7) is shown. The falsification error detection rate, the falsification miss rate, or the relationship thereof as a threshold determination criterion may be predetermined in the threshold determination unit 212 or may be input as a parameter by the user.

  FIG. 22 shows thresholds that are determined based on parameters when parameters indicating the level of probability of being determined to be falsified by a falsification detection device or the like are input by the user. For example, the user inputs one of severe / normal / sweet as a parameter to the threshold value determination device 20 together with the evaluation target data. When “severe” is input, the threshold value determination device 20 sets the threshold value low so as to increase the probability that the falsification detection device or the like determines that the falsification has occurred so that the falsification detection device or the like does not miss the falsification. . According to the example shown in the figure, a value belonging to a predetermined range smaller than 3.5 where the falsification miss rate = falsification false detection rate is determined as the threshold value. When “sweet” is input, the threshold value determination device 20 sets the threshold value higher so as to reduce the probability that the falsification detection device or the like determines that there has been falsification so that the falsification detection device or the like does not perform erroneous detection of falsification. To do. According to the example shown in the figure, a value belonging to a predetermined range larger than 3.5 where the falsification miss rate = falsification error detection rate is determined as the threshold value. When “normal” is input, a value that satisfies the falsification miss rate = falsification false detection rate is determined as the threshold value. According to such a configuration, the user can change the threshold value of whether or not tampering is specified by designating parameters according to the purpose of tampering detection by the tampering detection device or the like.

  The processing flow of the threshold determination device 20 has been described above. Next, based on FIGS. 23 to 25, the flow of processing of the accuracy evaluation apparatus 30 according to the present embodiment will be described. First, the flow of processing will be schematically described based on FIG. 23, and then detailed description will be given based on FIG. 24 and FIG.

  Each data necessary for accuracy evaluation of tampering detection by the tampering detection device or the like is input to the accuracy evaluation device 30 (step S302). Each data includes a test chart image before printing created by the evaluation target data creation device 10, a read image after falsification (falsified image), falsified area information, and a threshold value determined by the threshold value determination device 20.

  The falsification detection device or the like detects a falsified region using each input data (S304), and then the accuracy evaluation device 30 compares the result detected in step S304 with the falsified region information inputted. Thus, the accuracy of alteration detection by the alteration detection device or the like is obtained (S306). The outline of the processing flow has been described above.

  Next, a detailed description will be given. As shown in FIG. 24, the alteration region detection unit 304 of the accuracy evaluation device 304 acquires the test chart image 1002 and the alteration image 1007 before printing from the input unit 302, detects the alteration region from the alteration image 1007, The detection result is stored in the falsification detection result area storage unit 306. Specifically, in the falsification detection result area storage unit 306, information on coordinates specifying the area determined to be falsified by the falsification area detection unit 304 is stored as falsification detection result area information. In FIGS. 24 and 25, the region determined to be falsified in the falsified image 1007 is surrounded by a square, and reference numerals 3002-1, 3002-2. ... 3002-n (hereinafter referred to as falsification detection area 3002).

  After all the falsified areas are detected from the falsified image 1007 by the falsified area detection unit 304, the accuracy evaluation unit 308 evaluates the falsification detection accuracy of the falsified area detection unit 304. As shown in FIG. 25, the accuracy evaluation unit 308 includes all the falsification detection result region information stored in the falsification detection result region storage unit 306 and all the falsification region information stored in the falsification region storage unit 126. And the number of missed alterations and the number of false alterations detected by the alteration region detection unit 304 are acquired. In FIG. 25, the region stored in the falsified region storage unit 126 in the falsified image 1007, that is, image specifying information different from the test chart image 1002 is included, and the falsified regions are denoted by reference numerals 3004-1 and 3004-. 2,... 3004-n (hereinafter referred to as a falsified region 3004). The area where the falsification area detection unit 304 missed the falsification is specifically an area that is the falsification area 3004 but not the falsification detection area 3002 as illustrated. Further, the area where the falsification area detection unit 304 has detected false falsification is specifically an area that is the falsification detection area 3002 but not the falsification area 3004 as illustrated.

The accuracy evaluation unit 308 obtains the number of falsification misses and the number of falsification detection errors, calculates a falsification miss rate and a falsification error detection rate, and ends the falsification detection accuracy evaluation of the falsification detection device and the like. The falsification miss rate and falsification error detection rate can be calculated by the following equations.
Falsification miss rate (%) = Number of falsification misses / Number of falsification characters x 100
False alteration detection rate (%) = False alteration detection count / No alteration character count x 100
The functional configuration of the accuracy evaluation device 30 has been described above.

  According to the falsification detection threshold value determination system according to the present embodiment, the evaluation target data creation device 10 can create a plurality of evaluation target data whose presence or absence of falsification is known in advance from one test chart image. Therefore, in order to determine the threshold value of the alteration detection device, it is not necessary to manually create an image obtained by printing the image, or an image obtained by printing the image and falsified from a plurality of pre-print images. Work time can be shortened. In addition, since the evaluation object data creation apparatus 10 can designate font information for creating a test chart image, the evaluation object data can be created using text data of various designated fonts.

  In addition, since the optimum threshold value can be automatically determined by the threshold value determining device 20 according to the frequency distribution of the difference values of the image feature values, it is not necessary to search for the optimum threshold value by manually adjusting the threshold value and repeating the evaluation. The work time can be shortened, and an appropriate threshold value can be acquired as compared with the case of manual operation. Furthermore, since the user can input parameters to the threshold determination device 20, the threshold can also be determined so as to satisfy the detection accuracy desired by the user. In addition, by inputting evaluation target data created with text data of various fonts to the threshold value determination device, an optimum threshold value can be acquired for each font.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are of course within the technical scope of the present invention. Understood.

  The present invention can be applied to a device for detecting falsification and a system for evaluating accuracy of a program. In particular, a threshold value used for determining whether or not falsification is performed by a falsification detection device that performs falsification detection using an image feature amount or the like. Applicable to the system to decide.

It is a block diagram which shows the function structure of the evaluation object data creation apparatus concerning embodiment of this invention. It is a block diagram which shows the function structure of the threshold value determination apparatus in the embodiment. It is a block diagram which shows the function structure of the accuracy evaluation apparatus in the embodiment. It is explanatory drawing which shows the outline of the flow of a process of the evaluation object data creation apparatus in the embodiment. It is a flowchart which shows the outline of the flow of a process of the evaluation object data creation apparatus in the embodiment. It is explanatory drawing which shows the flow of a process of the evaluation object data creation apparatus in the embodiment in detail. It is explanatory drawing which shows the flow of a process of the evaluation object data creation apparatus in the embodiment in detail. It is explanatory drawing which shows the flow of a process of the evaluation object data creation apparatus in the embodiment in detail. It is explanatory drawing which shows the flow of a process of the evaluation object data creation apparatus in the embodiment in detail. It is explanatory drawing which shows the flow of a process of the evaluation object data creation apparatus in the embodiment in detail. It is explanatory drawing which shows the flow of a process of the evaluation object data creation apparatus in the embodiment in detail. It is explanatory drawing which shows the flow of a process of the evaluation object data creation apparatus in the embodiment in detail. It is a block diagram which shows the function structure of the evaluation object data creation apparatus concerning the modification of embodiment of this invention. It is explanatory drawing which shows in detail the flow of a process of the evaluation object data creation apparatus in the modification of the embodiment. It is explanatory drawing which shows in detail the flow of a process of the evaluation object data creation apparatus in the modification of the embodiment. It is explanatory drawing which shows the outline of the flow of a process of the threshold value determination apparatus in the embodiment. It is a flowchart which shows the outline of the flow of a process of the threshold value determination apparatus in the embodiment. It is explanatory drawing which shows the flow of a process of the threshold value determination apparatus in the embodiment in detail. It is explanatory drawing which shows the flow of a process of the threshold value determination apparatus in the embodiment in detail. It is explanatory drawing which shows the example of determination of the threshold value by the threshold value determination apparatus in the embodiment. It is explanatory drawing which shows the example of determination of the threshold value by the threshold value determination apparatus in the embodiment. It is explanatory drawing which shows the example of determination of the threshold value by the threshold value determination apparatus in the embodiment. It is a flowchart which shows the outline of the flow of a process of the accuracy evaluation apparatus in the embodiment. It is explanatory drawing which shows the flow of a process of the accuracy evaluation apparatus in the embodiment in detail. It is explanatory drawing which shows the flow of a process of the accuracy evaluation apparatus in the embodiment in detail. It is explanatory drawing which shows the example of embedding of the digital watermark in the embodiment. It is explanatory drawing which shows the example of embedding of the digital watermark in the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,40 Evaluation object data creation apparatus 20 Threshold value determination apparatus 30 Accuracy evaluation apparatus 102 Test chart generation part 104 Mark insertion part 106 Print output part 108 Reading part 110,410 Evaluation image generation part 112 Mark detection part 114 Position information calculation part 116 Image Cutout unit 118 Evaluation target data output unit 120 Region storage unit 122 Read image region storage unit 124 Tampered image creation unit 126 Tampered region storage unit 202 Evaluation target data input unit 204 Feature amount measurement unit 206 Feature amount difference calculation unit 208 Total object data storage Unit 210 Totaling Unit 212 Threshold Determination Unit 302 Input Unit 304 Tampering Area Detection Unit 404 Coordinate Information Embedding Unit 412 Coordinate Information Extracting Unit 414 Position Information Acquisition Unit 1002 Test Chart Image 1005 Read Image 1006 Evaluation Target Data 002 aggregate target data

Claims (13)

A falsification detection threshold value determination system for determining a threshold value for determining whether or not a print content of a printed matter has been falsified:
An area storage unit for storing a plurality of area information in which image specifying information of an arbitrary area of the printable original image and position information of the area are associated;
A mark insertion part for inserting a mark into at least two opposite corners of the four corners of the original image;
An image output unit for outputting an original image in which the mark is inserted;
A reading unit that reads a printed matter on which the output original image is printed, and creates a read image;
A mark detector for detecting position information where the mark is inserted from the read image;
A position information calculation unit that calculates position information of an area corresponding to an arbitrary area of the original image in the read image based on position information of an arbitrary area of the original image and position information of the mark;
An image cutout unit that cuts out an image of the arbitrary area from the original image based on position information of the arbitrary area of the original image, and cuts out an image of the area corresponding to the calculated position information from the read image; ;
An evaluation object data output unit for outputting evaluation object data including the cut out set of images and image specifying information of each image;
From the image specifying information of each image included in the evaluation target data, it is determined whether or not the image specifying information included in the set of images is the same, and based on the determination result and the set of images A threshold value determination unit for determining the threshold value;
A tampering detection threshold value determination system comprising: A falsification detection threshold value determination system for determining a threshold value for determining whether or not a print content of a printed matter has been falsified:
An area storage unit for storing a plurality of area information in which image specifying information of an arbitrary area of the printable original image and position information of the area are associated;
A coordinate information embedding unit that embeds the coordinate information in the original image in association with a point specified by the coordinates included in the position information;
An image output unit for outputting an original image in which the coordinate information is embedded;
A reading unit that reads a printed matter on which the output original image is printed, and creates a read image;
A coordinate information extraction unit that extracts the embedded coordinate information from the read image;
A position information acquisition unit that acquires position information of an area corresponding to an arbitrary area of the original image in the read image based on position information of an arbitrary area of the original image and the extracted coordinate information;
An image cutout unit that cuts out an image of the arbitrary area from the original image based on position information of the arbitrary area of the original image, and cuts out an image of the area corresponding to the acquired position information from the read image; ;
An evaluation object data output unit for outputting evaluation object data including the cut out set of images and image specifying information of each image;
From the image specifying information of each image included in the evaluation target data, it is determined whether or not the image specifying information included in the set of images is the same, and based on the determination result and the set of images A threshold value determination unit for determining the threshold value;
A tampering detection threshold value determination system comprising: The image cut out from the read image by the image cutout unit is an area on the read image specified by position information of an area corresponding to an arbitrary area of the original image, and the cut out image A falsified image creation unit that creates a falsified image by pasting in an arbitrary area different from the cut-out source;
A falsification area storage unit that stores position information of the pasting area;
The tampering detection threshold value determination system according to claim 1 or 2, further comprising: A feature quantity measuring unit that measures the feature quantities of each of the set of images included in the evaluation target data;
A feature amount difference calculation unit for obtaining a difference value between the measured feature amounts of the respective images;
Based on the image specifying information of each image included in the evaluation object data, a plurality of images are associated with either the first group in which the image specifying information of the set of images is the same or the second group that is not the same. A target data storage unit for storing the difference value;
Aggregation for creating a frequency distribution of the difference values associated with the first group and / or a frequency distribution of the difference values associated with the second group based on the storage contents of the aggregation target data storage unit Part and;
The falsification detection threshold value determination system according to any one of claims 1 to 3, wherein the threshold value determination unit determines the threshold value based on one or both of the frequency distributions. The falsification detection threshold value determination system according to any one of claims 1 to 4, further comprising a parameter input unit for inputting a parameter, wherein the threshold value determination unit further determines the threshold value based on the parameter. 6. The falsification detection threshold value determination system according to claim 5, wherein the parameter is a falsification error detection rate, a falsification miss rate, or a probability of determining that falsification has occurred. A falsification area detector that detects one or more falsification areas from the falsified image based on the original image, the falsified image, and the threshold;
The position information of the one or more falsified areas detected by the falsified area detection unit is compared with the position information of the pasted area, and the falsification detection by the falsified area detection unit is performed based on the comparison result. An accuracy evaluation unit for determining accuracy;
The tampering detection threshold value determination system according to claim 3, further comprising: An evaluation object data creation device that creates evaluation object data for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with:
An area storage unit that stores a plurality of area information in which image specifying information of an arbitrary area of the printable original image and position information of the area are associated;
A mark insertion part for inserting a mark into at least two opposite corners of the four corners of the original image;
An image output unit for outputting an original image in which the mark is inserted;
A reading unit that reads a printed matter on which the output original image is printed, and creates a read image;
A mark detection unit for detecting position information where the mark is inserted from the read image;
A position information calculation unit that calculates position information of an area corresponding to an arbitrary area of the original image in the read image based on position information of an arbitrary area of the original image and position information of the mark;
An image cutout unit that cuts out an image of the arbitrary area from the original image based on position information of the arbitrary area of the original image, and cuts out an image of the area corresponding to the calculated position information from the read image; ;
An evaluation object data output unit for outputting evaluation object data including the cut out set of images and image specifying information of each image;
An evaluation object data creation device characterized by comprising: An evaluation object data creation device that creates evaluation object data for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with:
An area storage unit for storing a plurality of area information in which image specifying information of an arbitrary area of the printable original image and position information of the area are associated;
A coordinate information embedding unit that embeds the coordinate information in the original image in association with a point specified by the coordinates included in the position information;
An image output unit for outputting an original image in which the coordinate information is embedded;
A reading unit that reads a printed matter on which the output original image is printed, and creates a read image;
A coordinate information extraction unit that extracts the embedded coordinate information from the read image;
A position information acquisition unit that acquires position information of an area corresponding to an arbitrary area of the original image in the read image based on position information of an arbitrary area of the original image and the extracted coordinate information;
An image cutout unit that cuts out an image of the arbitrary area from the original image based on position information of the arbitrary area of the original image, and cuts out an image of the area corresponding to the acquired position information from the read image; ;
An evaluation object data output unit for outputting evaluation object data including the cut out set of images and image specifying information of each image;
An evaluation object data creation device characterized by comprising: A threshold value determining device for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with:
An evaluation object data input unit for inputting evaluation object data including a set of images and image specifying information of each image;
A feature quantity measuring unit for measuring each feature quantity of the set of inputted images;
A feature amount difference calculation unit for obtaining a difference value between the measured feature amounts of the respective images;
Based on the image specifying information of each image included in the evaluation object data, a plurality of images are associated with either the first group in which the image specifying information of the set of images is the same or the second group that is not the same. A target data storage unit for storing the difference value;
Aggregation for creating a frequency distribution of the difference values associated with the first group and / or a frequency distribution of the difference values associated with the second group based on the storage contents of the aggregation target data storage unit Part;
A threshold value determining unit that determines the threshold value based on either or both of the frequency distributions;
A threshold value determining device comprising: An evaluation object data creation method for creating evaluation object data for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with:
An area storage step of storing a plurality of area information in the storage unit in association with image specifying information of an arbitrary area of the printable original image and position information of the area;
A mark insertion step of inserting marks at at least two opposite corners of the four corners of the original image;
An image output step of outputting an original image in which the mark is inserted;
A reading step of reading a printed matter on which the output original image is printed and creating a read image;
A mark detection step of detecting position information where the mark is inserted from the read image;
A position information calculating step of calculating position information of an area corresponding to an arbitrary area of the original image in the read image based on position information of an arbitrary area of the original image and position information of the mark;
An image cutout step of cutting out an image of the arbitrary area from the original image based on position information of an arbitrary area of the original image, and cutting out an image of an area corresponding to the calculated position information from the read image; ;
An evaluation object data output step for outputting evaluation object data including the cut out set of images and image specifying information of each image;
An evaluation target data creation method characterized by including: An evaluation object data creation method for creating evaluation object data for determining a threshold value for determining whether or not a print content of a printed matter has been tampered with:
An area storage step of storing a plurality of area information in the storage unit in association with image specifying information of an arbitrary area of the printable original image and position information of the area;
A coordinate information embedding step of embedding the coordinate information in the original image in association with a point specified by the coordinates included in the position information;
An image output step of outputting an original image in which the coordinate information is embedded;
A reading step of reading a printed matter on which the output original image is printed and creating a read image;
A coordinate information extraction step of extracting the embedded coordinate information from the read image;
A position information acquisition step of acquiring position information of an area corresponding to an arbitrary area of the original image in the read image based on position information of an arbitrary area of the original image and the extracted coordinate information;
An image cutout step of cutting out an image of the arbitrary area from the original image based on position information of an arbitrary area of the original image, and cutting out an image of an area corresponding to the acquired position information from the read image; ;
An evaluation object data output step for outputting evaluation object data including the cut out set of images and image specifying information of each image;
An evaluation target data creation method characterized by including: A threshold value determining method for determining a threshold value for determining whether or not a print content of a printed material has been tampered with:
An evaluation object data input step for inputting evaluation object data including a set of images and image specifying information of each image;
A feature amount measuring step of measuring each feature amount of the set of input images;
A feature amount difference calculating step for obtaining a difference value between the measured feature amounts of the images;
Based on the image specifying information of each image included in the evaluation object data, a plurality of images are associated with either the first group in which the image specifying information of the set of images is the same or the second group that is not the same. A tabulation target data storage step for storing the difference value in a storage unit;
Aggregation for creating a frequency distribution of the difference values associated with the first group and / or a frequency distribution of the difference values associated with the second group based on the storage contents of the aggregation target data storage unit Steps and;
A threshold value determining step for determining the threshold value based on one or both of the frequency distributions;
A method for determining a threshold value, comprising:

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